Crystalline silicon solar cell with Poly-Finger structure and preparation process of crystalline silicon solar cell

Abstract

The invention belongs to the technical field of solar cells, and particularly relates to a crystalline silicon solar cell with a Poly-Finger structure and a preparation process of the crystalline silicon solar cell. The preparation method comprises the following steps of: 1, sequentially forming a SiO2 tunneling oxide layer and a first N + poly layer with the thickness of 30nm-70nm on the back surface of a silicon wafer; step 2, forming a layer of SiO2 mask in a non-metal region on the back surface of the silicon wafer; 3, forming a second N + poly layer on the back surface of the silicon wafer; step 4, removing PSG in the non-metal region by laser; and 5, carrying out RCA cleaning on the battery piece, removing the poly layer on the front side and the side surface of the battery piece, and the second N + poly layer and the SiO2 mask in the non-metal area on the back side, and drying the battery piece. According to the preparation method provided by the invention, the thickness of the poly in the non-printing area can be accurately controlled, the poly-finger structure on the back surface of the battery is not influenced, and electric leakage of the battery is not caused.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and particularly relates to a preparation process of a crystalline silicon solar cell with a Poly-Finger structure. Background Art

[0002] With the rapid development of TOPCon crystalline silicon solar cell technology, continuously improving the photoelectric conversion efficiency is an eternal goal pursued unremittingly. As is well known, poly in TOPCon cells has strong parasitic absorption of light, thereby reducing the photoelectric conversion efficiency of the cells. However, poly also plays an important role in TOPCon cells. On the one hand, heavily phosphorus-doped poly is indispensable for realizing the tunneling effect and improving the passivation effect. On the other hand, poly in the metal region is the key to avoiding direct contact between the metal electrode and the silicon substrate, thereby reducing metal-semiconductor recombination. Therefore, the Poly-Finger process of retaining poly in the metal region and partially removing poly in the non-metal region has attracted more and more attention.

[0003] In the existing Poly-Finger structure of Topcon cells, high-power lasers are often directly used to open the PSG mold after the phosphorus diffusion process, and then RCA is used to partially remove poly in the non-metal region. However, this method has the following disadvantages: 1. It is difficult to control the thickness of poly in the non-printing area by using RCA wet method, and the process window is small, and it is easy to over-etch or not etch at all. Over-etching will cause the hindrance of electron lateral transmission, thereby resulting in the damage of FF; 2. By replacing the more protective RCA additives, the purpose of partially removing poly in the non-metal region can be achieved. However, due to the consistent structure of the side and front wrap plating and the back of TOPCON, replacing the RCA additives will cause the front and side wrap plating to be unable to be cleaned thoroughly, thereby resulting in the conduction and leakage of the PN junction of the cell, affecting the cell efficiency. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a preparation process of a crystalline silicon solar cell with a Poly-Finger structure to solve the problems in the prior art.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions.

[0006] The present invention provides a preparation process of a crystalline silicon solar cell with a Poly-Finger structure, including:

[0007] Step 1, forming a tunneling oxide layer and a first N poly layer with a thickness of 30 nm to 70 nm on the back surface of the silicon wafer in sequence; 2 The tunneling oxide layer and a first N poly layer with a thickness of 30 nm to 70 nm; + poly layer;

[0008] Step 2, forming a layer of SiO on the non-metal region of the back surface of the silicon wafer2 Mask;

[0009] Step 3: Form a second N + poly layer on the back side of the silicon wafer;

[0010] Step 4: Use laser to remove PSG in the non-metal area;

[0011] Step 5: Perform RCA cleaning on the solar cell to remove the poly layer on the front and side surfaces and the second N + poly layer and SiO 2 mask on the back non-metal area, and then dry.

[0012] In the present invention, by using a two-step poly layer formation and mask process, precise control of the thickness of the poly layer in the non-metal area can be achieved, enabling the formation of a poly-finger structure on the back of the cell without affecting the FF, and cleaning the plating around thoroughly without causing leakage. When the thickness of the first N + poly layer is too thick, the current increase of the poly-finger cell is less. When the thickness of the first N + poly layer is too thin, the path of electron lateral transport is restricted, making it difficult for electrons to be transported to the electrode. This means that more electrons cannot be effectively collected and utilized, resulting in energy loss and a decrease in the collection efficiency of the cell for photo-generated current.

[0013] In some embodiments of the present invention, the thickness of the second N + poly layer is 100 nm to 120 nm.

[0014] In some embodiments of the present invention, the P doping concentration in the first N + poly layer is 2E 20 cm -3 ~4E 20 cm -3 ; the P doping concentration in the second N + poly layer is 2E 20 cm -3 ~4E 20 cm -3 . When the doping concentration of P is too high, severe diffusion occurs in the silicon matrix, resulting in carrier recombination, thus causing a decrease in the open-circuit voltage and forming a whole-surface dark chip; when the doping concentration of P is too low, the passivation effect is poor, causing a decrease in the open-circuit voltage, and at the same time, a good ohmic contact cannot be formed between the poly and the electrode, so the fill factor will also decrease.

[0015] In some embodiments of the present invention, in Step 1 and Step 3, the first N + poly layer and the second N + poly layer are deposited by using PECVD technology.

[0016] In some embodiments of the present invention, in step one and step three, the doping source gas for the PECVD technology is SiH 4 and PH 3 gas.

[0017] In some embodiments of the present invention, in step one, the deposition time of the PECVD technology is 300 s to 400 s.

[0018] In some specific embodiments of the present invention, in step one, the flow rate of the SiH 4 is 1000 Sccm to 2000 Sccm, and the flow rate of the PH 3 is 150 Sccm to 400 Sccm. During the deposition of the first N + poly layer, the pressure is 100 mBar to 400 mBar. When the pressure and flow rate of the SiH 4 are too small, the deposition rate is too slow. When they are too large, the deposition rate is too fast and the film is loose; when the flow rate of the PH 3 is relatively small, it will cause insufficient content of P element in the poly layer, and it is impossible to form the N + layer, resulting in a decrease in the passivation effect, a low turn-on voltage. When the flow rate is large, there will be too much P element in the poly layer, which will diffuse into the silicon matrix in large quantities, resulting in serious carrier recombination, and thus both the turn-on voltage and the FF are low.

[0019] In some embodiments of the present invention, in step one, the deposition temperature of the first N + poly layer is 600 °C to 700 °C.

[0020] In some embodiments of the present invention, in step one, during the preparation of the first N + poly layer, the power of the alternating radio frequency power supply is 10 W to 1000 W. If the power of the power supply is too low, it will cause the reaction gas not to be ionized, so that deposition cannot be carried out. If the power is too high, the plasma energy is too strong, and the heating effect on the silicon matrix is too strong, which will cause the temperature of the silicon wafer to be too high, thus having a negative impact on the reaction.

[0021] In some embodiments of the present invention, in step three, the deposition time of the PECVD technology is 1000 s to 1300 s.

[0022] In some specific embodiments of the present invention, in step three, the flow rate of the SiH 4 is 1000 Sccm to 2000 Sccm, and the flow rate of the PH 3 is 150 Sccm to 400 Sccm. During the deposition of the second N + poly layer, the pressure is 100 mBar to 400 mBar.

[0023] In some embodiments of the present invention, in step three, the second N + The deposition temperature of the poly layer is 600°C to 700°C

[0024] In some embodiments of the present invention, in step one, the first N + During the preparation of the poly layer, the power of the alternating radio frequency power supply is 10 W to 1000 W.

[0025] In some embodiments of the present invention, in step one, the deposited SiO 2 The thickness of the tunneling oxide layer is 1 nm to 3 nm. In the present invention, when the thickness of the SiO 2 tunneling oxide layer is too high, its conductivity is poor, which will affect electron transport. When the SiO 2 tunneling oxide layer is too thin, phosphorus diffusion is likely to expand inward, resulting in an increase in carrier recombination.

[0026] In some specific embodiments of the present invention, in step one, when depositing the SiO 2 tunneling oxide layer, the deposition temperature is 400°C to 600°C.

[0027] In some embodiments of the present invention, during the deposition of the tunneling oxide layer, the flow rate of O 2 is 30000 Sccm to 40000 Sccm, and the deposition time is 400 s to 450 s.

[0028] In some embodiments of the present invention, in step two, the thickness of the SiO 2 mask is 5 μm to 7 μm. The SiO 2 mask protects the poly in the non-metal region from being completely washed away.

[0029] In some embodiments of the present invention, in step four, high-power laser is used to remove PSG in the non-metal region. Since SiO 2 has a blocking effect on phosphorus element doping, the laser will not cause serious inward diffusion to the silicon wafer. Specifically, the laser power is 240 W and the pulse energy is 300 μJ.

[0030] In some embodiments of the present invention, in step five, the RCA cleaning includes RCA pre-alkali cleaning, RCA post-alkali cleaning, and RCA acid cleaning; specifically, it includes:

[0031] (1) RCA pre-alkali cleaning, using NaOH / additive to clean the battery wafer to remove the poly layer plated around the front and side of the battery wafer and the second N + poly layer in the non-metal region on the back. Since the SiO 2 mask in the non-metal region does not react with NaOH, the first N +The poly layer is retained;

[0032] (2) Place the cleaned solar cell wafers in the first cleaning tank filled with deionized water;

[0033] (3) After RCA, perform alkaline cleaning. Place the solar cell wafers in NaOH / H 2 O 2 to remove the residue of the additive in step (1);

[0034] (4) Place the solar cell wafers in the second cleaning tank filled with deionized water;

[0035] (5) Perform RCA acid cleaning. Place the solar cell wafers in the acid cleaning tank filled with HF to remove the naturally oxidized SiO 2 on the surface and the SiO 2 mask in the non-metal area, and form a Si-H hydrophobic layer;

[0036] (6) Place the solar cell wafers in the third cleaning tank filled with deionized water;

[0037] (7) Place the solar cell wafers in slow lifting with deionized water;

[0038] (8) Place the solar cell wafers in the drying tank equipped with a blower and heating.

[0039] In some embodiments of the present invention, in step one, a tunneling oxide layer and a first N 2 poly layer are respectively deposited on the back of the silicon wafers after texturing and boron diffusion. + poly layer.

[0040] In some embodiments of the present invention, texturing is performed by etching with a low-concentration alkaline solution to form a uniformly sized pyramid structure on the single-crystalline silicon wafer; the low-concentration alkaline solution is a NaOH solution with a concentration of 1 wt% - 2 wt%; the texturing time is 450 s - 500 s, and the temperature is 60 °C - 70 °C.

[0041] In some embodiments of the present invention, the method of boron diffusion includes: using BCl 3 as a diffusion source to perform diffusion on the front of the silicon wafer, the diffusion temperature is 850 °C - 900 °C, and the sheet resistance is controlled at 230 Ω / □ - 250 Ω / □.

[0042] In some embodiments of the present invention, after step five, a passivation layer and an antireflection layer are further formed on the front and back of the silicon wafer, and metal paste is printed and sintered on the front and back metal areas to obtain a front metal electrode and a back metal electrode respectively.

[0043] The present invention also provides a poly-crystalline silicon solar cell with a Poly-Finger structure, which is prepared by using the above preparation process.

[0044] Based on the technical solution of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention utilizes a two-step poly layer formation and a masking process to achieve precise control of the poly thickness in the non-metal region, realizing the poly-finger structure on the back of the battery without affecting the FF, and cleaning the plating around thoroughly to avoid leakage. Description of the Drawings

[0046] Figure 1 It is the process flow chart of the preparation method provided in Embodiment 1 of the present invention.

[0047] Figure 2 It is the process flow chart of the Poly-Finger preparation method in Comparative Example 1. Detailed Embodiments

[0048] For the experimental methods without specific conditions in the following embodiments of the present invention, they are usually carried out according to conventional conditions or according to the conditions recommended by the manufacturer.

[0049] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0050] As used in the present invention, "a plurality of" means two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0051] The following is described in conjunction with specific embodiments.

[0052] Embodiment 1

[0053] A Poly-Finger process for TOPCON solar cells (the process flow chart is as Figure 1 shown) includes:

[0054] 1. Texturing: Etching with a low-concentration alkali solution to form uniformly sized pyramid structures on both sides of a single-crystalline silicon wafer (N-type single-crystalline silicon wafer, resistivity range of 0.9*10^-4~7.5*10^-4 / (Ω*m), thickness of 145 μm, size of 182*183.75 mm); controlling the low-concentration alkali solution (NaOH solution) at 2 wt%, the texturing time at 500 s, the texturing temperature at 60 °C, and the height at 1.3 μm.

[0055] 2. Use BCl 3 as a diffusion source to perform diffusion on the front side of the silicon wafer; the diffusion temperature is 850 °C, and the sheet resistance is controlled at 250 Ω / □.

[0056] 3. Polish the front side with a high-concentration alkali solution for polishing; the concentration of the high-concentration alkali solution is controlled at 6 wt%, the alkali polishing temperature is controlled at 60 °C, and the polishing time is controlled at 250 s.

[0057] 4. Use PECVD technology to deposit a 1.5 nm thick SiO 2 layer and a 30 nm thick first N + poly layer on the back side of the cell;

[0058] First, introduce O 2 into the cavity at 580 °C, with a flow rate of 36000 sccm and a deposition time of 450 s to form a 1.5 nm thick SiO 2 layer. In this step, the O 2 flow rate is 36000 sccm, and the cavity pressure is at atmospheric pressure; then evacuate the vacuum, and introduce SiH 4 , PH 3 gas into the cavity at 600 °C to form the first N + poly layer. During the formation of the first N + poly layer, the power of the AC radio frequency power supply is 500 W, the SiH 4 flow rate is 1600 sccm, the PH 3 flow rate is 280 sccm, the cavity pressure is 240 mBar, and the deposition time is 300 s. The P doping concentration of the formed first N + poly layer is 3E 20 cm -3 .

[0059] 5. Use screen printing technology to print a SiO mask about 6 μm thick in the non-metal area; 2

[0060] Screen printing technology parameters: the printing pressure is 85 N, the printing width is 40 μm, and the weight of the printing paste for the whole surface printing is 400 mg.

[0061] 6. Use PECVD technology to continue depositing a 100 nm thick second N + poly layer on the back side; introduce SiH 4 , PH 3 gas into the cavity at 600 °C to form the second N + poly layer. In this step, the power of the AC radio frequency power supply is 500 W, the SiH 4 flow rate is 1600 sccm, the PH 3The flow rate is 280 Sccm, the chamber pressure is 240 mBar, and the deposition time is 1000 s. The P doping concentration of the formed second N + poly layer is 3E 20 cm -3 .

[0062] 7. Use high-power laser to remove PSG in the non-metal area. Since the SiO 2 mask has a blocking effect on phosphorus doping, the laser will not cause serious internal diffusion to the silicon substrate. In this step, the laser power is 240 W and the pulse energy is 300 μJ.

[0063] 8. Alkaline cleaning before RCA. Use NaOH with a mass concentration of 5% to clean the solar cell to remove the poly layer wrapped around the front and side surfaces of the solar cell and the second N + poly layer in the non-metal area on the back. Since the SiO 2 mask in the non-metal area does not react with NaOH, the first N + poly layer under the mask is retained.

[0064] 9. Place the cleaned solar cell in cleaning tank one filled with deionized water to wash away the high-concentration NaOH adsorbed on the silicon wafer surface.

[0065] 10. Alkaline cleaning after RCA. Place the solar cell in NaOH / H 2 O 2 with a mass concentration of 5% for cleaning.

[0066] 11. Place the solar cell in cleaning tank two filled with deionized water and rinse for 90 s.

[0067] 12. Acid cleaning in RCA. Place the solar cell in the acid cleaning tank filled with HF with a volume concentration of 25% to remove the naturally oxidized SiO 2 on the surface and the SiO 2 mask in the non-metal area to form a Si-H hydrophobic layer.

[0068] 13. Place the solar cell in cleaning tank three filled with deionized water and rinse for 90 s.

[0069] 14. Place the solar cell in the slow lifting tank filled with deionized water and rinse again for 30 s to wash away the acid residue in step 12, and then slowly pull it out; then place the solar cell in the drying tank equipped with a blower and heating, and dry it at 95 °C for 700 s.

[0070] 15. Using ALD technology, deposit an aluminum oxide film with a thickness of 4 nm on the front side of the cell. Then, perform PECVD on the cell to coat the front and back sides with an SiNx antireflection film, with a thickness of 74 nm on the front side and 79 nm on the back side. Subsequently, make the metal paste form a good ohmic contact with the silicon wafer to achieve metallization and produce the finished cell.

[0071] Example 2

[0072] A Poly-Finger process for TOPCON solar cells includes:

[0073] 1. Texturing: Etch using a low-concentration alkali solution to form uniformly sized pyramid structures on both sides of a monocrystalline silicon wafer (N-type monocrystalline silicon wafer, resistivity range of 0.9*10^-4 - 7.5*10^-4 / (Ω*m), thickness of 145 μm, size of 182*183.75 mm). The low-concentration alkali solution (NaOH solution) is controlled at 1 wt%, the texturing time is controlled at 500 s, the texturing temperature is controlled at 70 °C, and the height is 1.3 μm.

[0074] 2. Use BCl 3 as a diffusion source to perform diffusion on the front side of the silicon wafer; the diffusion temperature is 900 °C, and the diffusion sheet resistance is controlled at 250 Ω / SP.

[0075] 3. Polish the front side using a high-concentration alkali solution for polishing; the high-concentration alkali solution concentration is controlled at 6 wt%, the alkali polishing temperature is controlled at 65 °C, and the polishing time is controlled at 250 s.

[0076] 4. Use PECVD technology to deposit a 1-nm-thick SiO 2 layer and a 50-nm-thick first N + poly layer on the back side of the cell;

[0077] First, introduce O 2 into the chamber at 400 °C, with a flow rate of 30000 Sccm and a deposition time of 400 s to generate a 1-nm-thick SiO 2 layer. In this step, the O 2 flow rate is 36000 Sccm, and the chamber pressure is at atmospheric pressure; then evacuate the chamber, and introduce SiH 4 , PH 3 gases into the chamber at 600 °C to form the first N + poly layer. During the formation of the first N + poly layer, the AC RF power supply power is 10 W, the SiH 4 flow rate is 1000 Sccm, the PH 3 flow rate is 150 Sccm, the chamber pressure is 240 mBar, and the deposition time is 350 s. The formed first N +The P doping concentration of the poly layer is 3E 20 cm -3 。

[0078] 5. Use screen printing technology to print a layer of SiO about 5 μm thick in the non-metal area 2 mask;

[0079] Screen printing technology parameters: printing pressure is 80 N, printing width is 35 μm, and the weight of the printing paste for the whole surface is 400 mg.

[0080] 6. Use PECVD technology to continue depositing a second N + poly layer with a thickness of 110 nm on the back; Introduce SiH 4 , PH 3 gas into the cavity at 600 °C to form the second N + poly layer. In this step, the power of the AC RF power supply is 10 W, the flow rate of SiH 4 is 1000 Sccm, the flow rate of PH 3 is 150 Sccm, the cavity pressure is 100 mBar, and the deposition time is 1300 s. The P doping concentration of the formed second N + poly layer is 2E 20 cm -3 。

[0081] 7. Use high-power laser to remove PSG in the non-metal area. Since the SiO 2 mask has a blocking effect on phosphorus element doping, the laser will not cause serious internal diffusion to the silicon substrate; In this step, the laser power is 240 W and the pulse energy is 300 μJ.

[0082] 8. RCA pre-alkali cleaning. Use 5% NaOH by mass concentration to clean the battery wafers to remove the poly layer around the front and side of the battery wafers and the second N + poly layer in the non-metal area on the back. Since the SiO 2 mask in the non-metal area does not react with NaOH, the first N + poly layer under the mask is retained.

[0083] 9. Place the cleaned battery wafers in cleaning tank one filled with deionized water to wash away the high-concentration NaOH adsorbed on the silicon wafer surface.

[0084] 10. RCA post-alkali cleaning. Place the battery wafers in 5% NaOH / H 2 O 2 for cleaning.

[0085] 11. Place the battery wafers in cleaning tank two filled with deionized water and rinse for 90 s.

[0086] 12. RCA pickling: Place the solar cell in a pickling tank filled with HF with a volume concentration of 25% to remove the naturally oxidized SiO on the surface 2 and the SiO in the non-metallic region 2 mask to form a Si-H hydrophobic layer.

[0087] 13. Place the solar cell in the third cleaning tank filled with deionized water and rinse for 90 s.

[0088] 14. Place the solar cell in a slow-lifting tank filled with deionized water and rinse again for 30 s to wash away the acid residue in step 12, and then slowly pull it out. After that, place the solar cell in a drying tank equipped with a blower and heating, and dry it at 95 °C for 700 s.

[0089] 15. Deposit a 4-nm-thick aluminum oxide film on the front side of the solar cell using ALD technology, and perform PECVD on the front and back sides of the solar cell to deposit an SiNx antireflection film, with 74 nm on the front side and 79 nm on the back side. Then, make the metal paste form a good ohmic contact with the silicon wafer to achieve metallization and produce the finished solar cell.

[0090] Example 3

[0091] A Poly-Finger process for TOPCon solar cells, including:

[0092] 1. Texturing: Etch using a low-concentration alkali solution to form uniformly sized pyramid structures on both sides of a single-crystalline silicon wafer (N-type single-crystalline silicon wafer, resistivity range of 0.9×10⁻⁴~7.5×10⁻⁴ / (Ω·m), thickness of 145 μm, size of 182×183.75 mm); control the low-concentration alkali solution (NaOH solution) at 1 wt%, the texturing time at 500 s, the texturing temperature at 70 °C, and the height at 1.3 μm.

[0093] 2. Use BCl 3 as a diffusion source to perform diffusion on the front side of the silicon wafer; the diffusion temperature is 900 °C, and the diffusion sheet resistance is controlled at 250 Ω / □.

[0094] 3. Polish the front side using a high-concentration alkali solution for polishing; control the high-concentration alkali solution at 6 wt%, the alkali polishing temperature at 65 °C, and the polishing time at 250 s.

[0095] 4. Use PECVD technology to deposit a 1-nm-thick SiO 2 layer and a 50-nm-thick first N + poly layer on the back side of the solar cell;

[0096] First, introduce O into the cavity at 400 °C2 , with a flow rate of 40000 Sccm, a deposition time of 400 s, to generate a 1-nm-thick SiO 2 layer. In this step, the O 2 flow rate is 36000 Sccm, and the chamber pressure is atmospheric pressure; then evacuate the chamber, and introduce SiH 4 , PH 3 gas into the chamber at 600 °C to form the first N + poly layer. During the formation of the first N + poly layer, the power of the AC RF power supply is 1000 W, the SiH 4 flow rate is 2000 Sccm, the PH 3 flow rate is 400 Sccm, the chamber pressure is 400 mBar, and the deposition time is 200 s. The P doping concentration of the formed first N + poly layer is 4E 20 cm -3 .

[0097] 5. Use screen printing technology to print a SiO mask about 5 μm thick in the non-metal area; 2 Screen printing technology parameters: the printing pressure is 80 N, the printing width is 35 μm, and the weight of the printing paste for the whole surface is 400 mg.

[0098] 6. Use PECVD technology to continue depositing a 110-nm-thick second N

[0099] poly layer on the back; introduce SiH + , PH 4 gas into the chamber at 600 °C to form the second N 3 poly layer. In this step, the power of the AC RF power supply is 1000 W, the SiH + flow rate is 1000 Sccm, the PH 4 flow rate is 150 Sccm, the chamber pressure is 100 mBar, and the deposition time is 1300 s. The P doping concentration of the formed second N 3 poly layer is 4E + cm 20 . -3 .

[0100] 7. Use high-power laser to remove PSG in the non-metal area. Since the SiO 2 mask has a blocking effect on phosphorus element doping, the laser will not cause serious internal diffusion to the silicon substrate; in this step, the laser power is 240 W and the pulse energy is 300 μJ.

[0101] 8. RCA pre-alkali cleaning: The solar cell wafers are cleaned with 5% NaOH by mass concentration to remove the poly layer around the front and side surfaces of the wafers and the second N poly layer in the non-metallic area on the back. Since the SiO mask in the non-metallic area does not react with NaOH, the first N poly layer under the mask is retained. + The poly layer 2 Since the SiO + mask in the non-metallic area does not react with NaOH, the first N

[0102] 9. Place the cleaned solar cell wafers in cleaning tank one filled with deionized water to wash away the highly concentrated NaOH adsorbed on the surface of the silicon wafers.

[0103] 10. RCA post-alkali cleaning: Place the solar cell wafers in 5% NaOH / H 2 O 2 for cleaning.

[0104] 11. Place the solar cell wafers in cleaning tank two filled with deionized water and rinse for 90 s.

[0105] 12. RCA acid cleaning: Place the solar cell wafers in an acid cleaning tank filled with 25% HF by volume concentration to remove the naturally oxidized SiO on the surface and the SiO mask in the non-metallic area, forming a Si-H hydrophobic layer. 2 and the SiO 2 mask in the non-metallic area, forming a Si-H hydrophobic layer.

[0106] 13. Place the solar cell wafers in cleaning tank three filled with deionized water and rinse for 90 s.

[0107] 14. Place the solar cell wafers in a slow-lift tank filled with deionized water and rinse again for 30 s to wash away the acid residue from step 12, then slowly take them out. After that, place the solar cell wafers in a drying tank equipped with a blower and heating, and dry them at 95 °C for 700 s.

[0108] 15. Deposit a 4-nm-thick aluminum oxide film on the front surface of the solar cell wafers using ALD technology, and deposit SiNx antireflection films on both the front and back surfaces of the solar cell wafers by PECVD, with 74 nm on the front and 79 nm on the back. Then, make the metal paste form a good ohmic contact with the silicon wafers to achieve metallization and produce finished solar cell wafers.

[0109] Example 4

[0110] In the preparation process of the poly-crystalline silicon solar cell with the poly-finger structure provided in Example 4, compared with Example 1, the difference is that the P doping concentration of the first N + poly layer is different, and the other steps are the same. Specifically, the P doping concentration of the first N + poly layer is 5E 20 cm -3 .

[0111] Preparation conditions: In the 4th step of Example 1, change the PH 3 flow rate to 500 Sccm, and the remaining steps are the same as those in Example 1.

[0112] Example 5

[0113] In the preparation process of the polycrystalline silicon solar cell with a poly-finger structure provided in Example 5, compared with Example 1, the difference is that the second N + poly layer has a different thickness, and the remaining steps are the same. The remaining steps are the same. Specifically, the second N + poly layer has a thickness of 80 nm.

[0114] Preparation conditions: In the 6th step of Example 1, change the deposition time to 800 s, and the remaining steps are the same as those in Example 1.

[0115] Example 6

[0116] In the preparation process of the polycrystalline silicon solar cell with a poly-finger structure provided in Example 6, compared with Example 1, the difference is that the second N + poly layer has a different P doping concentration, and the remaining steps are the same. Specifically, the second N + poly layer has a P doping concentration of 1E 20 cm -3 .

[0117] Preparation conditions: In the 6th step of Example 1, change the PH 3 flow rate to 120 Sccm, and the remaining steps are the same as those in Example 1.

[0118] Comparative Example 1

[0119] A preparation process of a TOPCON solar cell (as shown in the process flow chart Figure 2 ), including:

[0120] 1. Texturing, using a low-concentration alkali solution for etching to form uniformly sized pyramid structures on both sides of a monocrystalline silicon wafer (N-type monocrystalline silicon wafer, resistivity range of 0.9*10^-4~7.5*10^-4 / (Ω*m), thickness of 145 μm, size of 182*183.75 mm); the low-concentration alkali solution is controlled at 2 wt%, the texturing time is controlled at 500 s, the texturing temperature is controlled at 60 °C, and the height is 1.3 μm.

[0121] 2. Using BCl 3 as a diffusion source to perform diffusion on the front side of the silicon wafer, the diffusion temperature is 850 °C, and the diffusion sheet resistance is controlled at 250 Ω / SP.

[0122] 3. The high-concentration alkali solution for polishing is used to polish the front side; the high-concentration alkali solution is controlled at 6 wt%, the alkali polishing temperature is controlled at 60 °C, and the polishing time is controlled at 250 s.

[0123] 4. Use the LPCVD technology to deposit a 1.5-nm-thick SiO on the back side of the silicon wafer. 2 , the deposition temperature is 590 °C, then deposit 30 nm thick poly, the deposition temperature is 610 °C, and then use POCl 3 as the phosphorus source for phosphorus diffusion, and the diffusion sheet resistance is controlled at 60 Ω / sq;

[0124] 5. Use high-power laser to remove PSG in the non-metal area; in this step, the laser power is 240 W and the pulse energy is 300 μJ;

[0125] 10. After RCA, perform alkali washing, and place the cell in NaOH / H with a mass concentration of 5%. 2 O 2 for cleaning;

[0126] 11. Place the cell in cleaning tank two filled with deionized water and rinse for 90 s.

[0127] 12. Perform RCA acid washing, place the cell in the acid washing tank filled with HF with a volume concentration of 25% to remove the naturally oxidized SiO on the surface. 2 , and form a Si-H hydrophobic layer;

[0128] 13. Place the cell in cleaning tank three filled with deionized water and rinse for 90 s.

[0129] 14. Place the cell in the slow lifting tank filled with deionized water, rinse again for 30 s to wash away the acid residue in step 12, and then slowly pull it out; then place the cell in the drying tank equipped with a blower and heating, and dry it at 95 °C for 700 s.

[0130] 15. Use the ALD technology to deposit a 4-nm-thick aluminum oxide film on the front side of the cell, perform PECVD on the front and back sides of the cell to deposit SiNx antireflection films, 74 nm on the front side and 79 nm on the back side. Then make the metal paste form a good ohmic contact with the silicon wafer to achieve metallization and make the finished cell.

[0131] Comparative Example 2

[0132] For the preparation process of the crystalline silicon solar cell with the Poly-Finger structure provided in Comparative Example 2, compared with Example 1, the difference is that the thickness of the first N + poly layer is different, and the other steps are the same. Specifically, the thickness of the first N + poly layer is 80 nm.

[0133] Preparation conditions: Change the deposition time in the 4th step of Example 1 to 800 s, and keep the other steps the same as in Example 1.

[0134] Performance test:

[0135] Before metallization, perform minority carrier lifetime (Lifetime) test and SunsVoc test on the solar cells. After the solar cells are prepared, perform performance tests. The test results are shown in Tables 1 to 3.

[0136] Table 1 Minority carrier lifetime (Lifetime) test results of Examples 1 to 6 and Comparative Examples 1 to 2

[0137]

[0138] Note: Jo represents the reverse saturation current density; I-V oc _ represents the theoretical maximum open circuit voltage before the solar cell is printed; I-FF represents the fill factor; Gap in the table represents the difference between the parameters of the solar cell obtained by using the Poly-Finger preparation method disclosed in this application and the parameters of the solar cell obtained by using the Poly-Finger preparation method in the prior art.

[0139] Table 2 SunsVoc test results of Examples 1 to 6 and Comparative Examples 1 to 2

[0140]

[0141] Note: Voc represents the open circuit voltage; pFF represents the pseudo fill factor excluding the influence of series resistance; Jo1 represents the reverse saturation dark current density generated by the recombination of the base region and the emitter region; Gap in the table represents the difference between the parameters of the solar cell obtained by using the Poly-Finger preparation method disclosed in this application and the parameters of the solar cell obtained by using the Poly-Finger preparation method in the prior art.

[0142] Table 3 Electrical performance test results of Examples 1 to 6 and Comparative Examples 1 to 2

[0143]

[0144] Note: In the table, Eta (efficiency) represents the proportion of the solar cell converting solar energy into electrical energy; Uoc represents the open circuit voltage; Isc represents the short circuit current; FF represents the fill factor.

[0145] Gap in the table represents the difference between the parameters of the solar cell obtained by using the Poly-Finger preparation method disclosed in this application and the parameters of the solar cell obtained by using the Poly-Finger preparation method in the prior art.

[0146] As can be seen from Tables 1 to 3, the Lifetime test results of Examples 1 to 6 are improved compared to the Comparative Examples, mainly reflected in the improvement of I-FF, Voc and the decrease of Jo. It can be seen that when the thickness or P doping concentration of the first N + poly layer and the second N + poly layer change, it will affect the carrier recombination, resulting in a low minority carrier lifetime and an increase in J0. According to the SunsVoc test results, it is found that the test results of Examples 1 to 6 are improved compared to the Comparative Examples. It is mainly reflected in the improvement of Voc, pFF and the decrease of Jo. It can be seen that when the thickness or P doping concentration of the first N + poly layer and the second N + poly layer change, it will affect the passivation effect, resulting in a decrease in Uoc and an increase in J0. According to the battery performance test results, it is found that the battery performance test results of Examples 1 to 6 are improved compared to the Comparative Examples. It is mainly reflected in the improvement of Eta, Uoc, and Isc. It can be seen that when the thickness or P doping concentration of the first N + poly layer and the second N + poly layer change, it will cause a decrease in the passivation effect, an increase in recombination or a deterioration in contact, resulting in a decrease in Uoc, Isc, and FF, thus leading to a decrease in efficiency.

[0147] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0148] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A process for preparing a crystalline silicon solar cell with a Poly-Finger structure, characterized in that: include: Step 1: Form a SiO2 tunneling oxide layer and a 30nm~70nm thick first N + Poly layer; Step 2, forming a SiO2 mask on the non-metallic area on the back of the silicon wafer; Step 3: Form a second N on the back of the silicon wafer + Poly layer; Step 4: laser removal of PSG in non-metallic areas; Step 5: RCA cleaning of the cell to remove the poly layer on the front and side and the second N layer on the non-metallic area on the back. + poly layer and SiO2 mask, dry.

2. The preparation process according to claim 1, characterized in that: The second N + The thickness of the poly layer is 100nm~120nm.

3. The preparation process according to claim 1, characterized in that: The first N + The P doping concentration in the poly layer is 2E 20 cm -3 ~4E 20 cm -3 ; The second N + The P doping concentration in the poly layer is 2E 20 cm -3 ~4E 20 cm -3 .

4. The preparation process according to claim 1, characterized in that: In step 1 and step 3, the first N + poly layer and the second N + The poly layer is deposited using PECVD technology.

5. The preparation method according to claim 4, characterized in that: In step 1 and step 3, the doping source gases of the PECVD technology are SiH4 and PH3 gases.

6. The preparation method according to claim 5, characterized in that: In step 1, the deposition time of PECVD technology is 300s~400s.

7. The preparation method according to claim 5, characterized in that: In step three, the deposition time of PECVD technology is 1000s~1300s.

8. The preparation process according to claim 1, characterized in that: In step 2, the thickness of the SiO2 mask is 5 μm to 7 μm.

9. The preparation process according to claim 1, characterized in that: RCA cleaning includes RCA pre-alkali cleaning, RCA post-alkali cleaning, and RCA acid cleaning.

10. A crystalline silicon solar cell with a Poly-Finger structure, characterized in that: The method is prepared by the preparation process according to any one of claims 1 to 9.

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